Electric auxiliary drive for a travelling device primarily driven, in particular drawn or pushed, by human or animal power

ABSTRACT

An auxiliary drive for a travelling device has a boosting effect when the driving power requirements are high and has a regenerative effect when the driving power requirements are low or negative. The auxiliary drive is provided with a measurement device for the primary driving power and with a control that increases or diminishes the generated torque by reducing or increasing the regenerative braking torque when a predetermined primary driving force is exceeded or not reached, respectively. The use of regenerative braking to charge the batteries allows small and relatively light batteries to be used.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to an electric auxiliary drive for a travellingdevice primarily driven, in particular drawn or pushed, by human oranimal power.

2. Description of the Related Art

The field of application of the invention is, for example, that of golfcaddies and industrial carts, but much more besides.

For the two-wheeled or three-wheeled golf caddies normally drawn orpushed by the user, with a golf bag or the like clipped on them,electric drives of the wheels are also known. They are generallycontrolled, as required, by means of an adjusting lever arranged closeto the handle of the golf caddie. The battery required is thus designedto be sufficient in any case for an average round of 18 holes.Consequently, however, it is of a not inconsiderable weight, which makeshandling it, or the golf caddie, more difficult, and in some casesimpossible, in particular on uneven ground.

SUMMARY OF THE INVENTION

The object of the invention is to provide an energy-saving drive whichis altogether easier to handle and is also convenient to use.

According to the invention, this object is achieved by an electricauxiliary drive for a travelling device primarily driven, inparticularly drawn or pushed, by human or animal power, which has aboosting effect whenever the driving force,requirements are high and hasa regenerative effect whenever the driving force, requirements are low,in particular negative, and is provided with a measuring device for theprimarily exerted driving force, and with a control such that, whenevera predetermined primary driving force, is exceeded or not reached, saidcontrol resets the predetermined primary driving force, by increasing orreducing the generated torque or by reducing or increasing theregenerative braking torque.

The invention thus assumes a basic load carried by the user himself,which can be set at a comfortable level and spares the user from majorexertion. Since, on the other hand, energy is saved compared to a fullpower drive, a lighter battery is sufficient. The battery can be all thelighter since, apart from the efficiency-determined loss, energy usedwhen going uphill is recovered when going downhill and, moreover, evenwhen on level ground it is always charged to a certain extent, providedthat the internal losses or losses due to unevennesses of the ground donot use up the predetermined primary driving force. Furthermore, thecontrol is automated and does not require actuation. In favorableoperating conditions, the losses occurring can be fully compensated andthere is no need for external charging of the battery. Consequently,there is also no need for the infrastructure otherwise always requiredfor battery-operated vehicles.

The predetermined primary driving force which the human or animal has toapply can preferably be changed arbitrarily and/or by a control program.

Thus, for example in the case of a golf caddie, it can be set as desiredto 10 to 15N and can be reduced after a certain time by a controlprogram in order to compensate for increasing fatigue. It may be reducedwhen going uphill, when the user's own body weight makes him exerthimself more, or else be increased in order to remain truer to naturalconditions. It may also be increased when going down steeper inclines;the pull on the golf caddie then reduces the abrupt stopping of the bodymovement with each step. However, due to the limit of the regenerativebraking effect, it may be necessary for the user himself also to performbraking. In this case, it may even be provided to switch over to powerbraking. If appropriate, the predetermined primary driving force mayalso be greatly increased considering the charging state of the battery.

Particularly suitable for the auxiliary drive according to the inventionare three-phase synchronous motors. They can be controlled well and canoperate in reverse as a dynamo.

According to a further advantageous refinement of the invention, twocoaxial wheels are in each case provided with a motor and areindividually controlled, the proportions of the primary driving forcegoing to the different wheels being determined from a measurement of abending moment or a transverse force occurring in a device frame. Atorque exerted by the wheels on the device frame or via the device frameon the wheels produces corresponding bending moments and transverseforces in the device frame. The separate control of the wheels alsomakes it easier to move in a curve, in particular turning in place. Thisadvantage comes into full effect, for example, in the case of industrialcarts, which, for instance in warehouses, are used only on level ground.Furthermore, with this type of use, however, the boosting andregenerative braking always associated with the auxiliary driveaccording to the invention are also effective during starting andstopping.

The measuring of a bending moment occurring in the frame is possible,for example, in a very simple way with a plurality of strain gagesattached to various suitable points of a draw bar, which the framegenerally has in some form or other.

The simple drawing or pushing force may also be measured in a verysimple way by means of at least one strain gage attached at a bend ofthe draw bar, preferably at the bend of the draw bar forming the handle.A stronger drawing force extends the bend more, admittedly onlyextremely slightly, but perceptibly for the strain gage.

A particularly favorable type of design which the invention allows byvirtue of the reduced battery size is that two wheels with gearlesslyintegrated motors are arranged on an axle of the form of an elongatecase, in which the batteries are housed, and if appropriate the controlis housed. In this case, the batteries are scarcely evident.

Yet another step in this direction is that the wheels are equipped withintegrated motors, preferably gearless, and with in each case their own,integrated batteries, preferably furthermore with the associatedcontrol.

The integration of the batteries into the wheels together with themotors means that, unlike in the case of simple integration of themotors, there is no need for energy transmission connections of thewheels. With the exception of the control connections and the connectionto the measuring device, the wheels are absolutely independent units.This is made possible by the reduction of the required battery capacityassociated with the invention, while always maintaining an adequatecharging state.

The wheels with integrated motor need only then to be arranged on axlejournals which can be fastened by means of rotationally secure plugconnections. According to an advantageous development of the invention,combined with the mechanical plug connections are electric plugconnections for the lines leading into the wheel, i.e. control lines andenergy supply lines in the case of the wheels with only integratedmotors, and only control lines in the case of the wheels with integratedmotor and integrated batteries.

Measuring devices, possible in principle, for the primary driving forcehave already been mentioned above. Preferably, however, for measuringthe primary driving force if appropriate also the torque, a measuringunit is arranged in a device frame at a point, preferably a crosspointof the frame structure, through which the entire flow of force of theprimary driving force passes, preferably between a handle and a draw baror at the other end of the draw bar. This concentration of themeasurement in a separate unit built into the frame structure isexpedient in terms of production engineering and, in addition, makes itpossible to create favorable conditions, particularly for themeasurement. In this respect, it is proposed as a further advantageousdevelopment of the invention that the measuring unit comprises a moldingwhich is preferably embedded in a plastics compound and on whichclearances are used to create webs where bending stresses areconcentrated, to which strain gages are attached. Pairs of strain gagesare proposed, which are arranged next to one another in such a way thatthe one strain gage is stretched when the other is compressed, and whichare connected in a bridge circuit. Consequently, unbalances are largelycompensated. The embedding of the measuring unit may likewise beincorporated in a force-transmitting manner into the frame structure.Consequently, the said molding can be protected against overloads, inparticular with regard to force transmissions in a direction other thanthe intended bending stresses, in particular transversely thereto.

For implementing the design of the invention on a golf caddie, it isproposed that the said case is arranged as a central body of a mountingfor the golf bag, having two bars extending rigidly from it, whichconverge, at the end are angled upward and away from each other and arecontinued by a draw bar which at its end is provided with a handle, andhaving a carrying rack which is fastened at two joints on it and can beswung out of a supporting position up against the two bars, and that themeasuring unit is arranged at the transition between the said bars andthe draw bar or between the latter and the handle. This is aparticularly lightweight configuration appropriate for the driveaccording to the invention and made possible by the invention in thecase of a golf caddie which in any case is partially driven.

Golf caddies and industrial carts have already been mentioned asconstituting the field of application of the invention. To be expresslymentioned here as industrial carts which come into consideration arethose for mail delivery and also shopping carts, as well as wheelchairs,bicycles, rickshaws and also bicycle rickshaws.

The drawings reproduce by example an embodiment of the invention.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 schematically shows a golf caddie in plan view,

FIG. 2 shows a draw bar of the golf caddie in plan view on an enlargedscale,

FIG. 3 shows a further golf caddie in isometric representation,

FIG. 4 shows, slightly modified, a detail from FIG. 3,

FIGS. 5 and 6 together show a wheel of the golf caddie according to FIG.3,

FIG. 7 shows a handle of another golf caddie in elevation,

FIG. 8 shows an inner component part of the handle according to FIG. 7on an enlarged scale,

FIG. 9 shows bridge circuits formed by strain gages,

FIG. 10 shows a functional diagram of an auxiliary drive

FIG. 11 shows a wheel in an axial section and

FIG. 12 shows a section along line X--X in FIG. 9.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A device frame 3, substantially comprising a draw bar 1 and a cross-bar2, has at the ends of the cross-bar 2 two wheels 5, in each caseprovided with a three-phase synchronous motor 4. Arranged on the centerof the cross-bar 2 are a battery 6 and a control device 7. On the handle8 of the draw bar i there is a measuring device 9. A golf bag 10 isindicated in outline by dash-dotted lines.

The measuring device 9 comprises two strain gages 11 and 12, attached onthe right and left in the bend of the handle 8. Two further strain gages13 and 14 are attached on the right and left at the rear end of the drawbar 1.

The strain gages 11 and 12 are arranged in each case in a bridgecircuit. The voltages of the two bridges are calculated respect to eachother in the control device. This produces the basic loading of the twothree-phase synchronous motors 4.

The strain gages 13 and 14 are likewise arranged in each case in abridge circuit, and the voltages are calculated respect to each other inthe control device. With the value obtained therefrom, the basic loadingis distributed to the two three-phase synchronous motors according toconditions.

In detail:

When pulling straight ahead, because of the leverage of the handle 8 andthe bending stress produced as a result in the region of the measuringdevice 9, the strain gage 12 is stretched and the strain gage 11 iscompressed. If a limit is exceeded, the three-phase synchronous motors 4fed by the battery 6 are switched on. This may be an on-off circuit.Preferably, however, a torque dependent on the pulling force isgenerated. The same applies for pushing, with the reverse situation thatthe strain gage 11 is stretched and the strain gage 12 is compressed.

If in addition to the pulling there is turning, a torque is produced inthe frame 3. A bending stress is imparted to the draw bar I with respectto the cross-bar 3. Depending on the direction of turning, the straingage 13 is stretched and the strain gage 14 is compressed, or viceversa. The voltage value obtained therefrom distributes the basicloading, predetermined by the measuring device 9, differently to the twothree-phase synchronous motors 4 in a compensating manner. Thisdistribution is also preferably quantitatively determined as a functionof the torque.

Below the limit value at which the auxiliary drive is cut in, thethree-phase synchronous motors are switched as generators to batterycharging. In this case, the same pulling force is preferably always set,irrespective of the incline of the path being travelled, bycorresponding charging work and consequently braking of the wheels.

The paired arrangement of the strain gages 11 and 12 and also 13 and 14,the voltages of which are calculated with respect to each other, largelyexcludes unbalances. The output signal is increased.

The golf caddie according to the FIG. 3 has two wheels 22 on an axle 21in the form of a case. Integrated into the wheels 22 are motors, whichare fed by batteries housed in the axle 21 in the form of a case. Twobars 23, rigidly fastened on the axle 21, are angled at their free ends24 outward and upward and are connected by a measuring unit 25, which isadjoined by a draw bar 27 provided with a handle 26. Also attached onthe axle 21, at two joints 28, is a carrying rack 29. In the positiondrawn, it is supported on the axle 21 by ends protruding beyond thejoints 28 and can be swung up against the bars 23. A golf bag, supportedby its bottom on an upwardly angled-off end section 30 of the carryingrack 29, can be placed on a strap 31, fitted just above said rack, andin between the ends 24 of the bars 23. FIG. 4 shows the axle 21 in theform of a case, with the modification that the ends of the case aretapered in approximately pyramid form. This produces a favorable flow offorces, with a socket 32 respectively formed in the taper for an axlejournal 33 of one of the two wheels 22. At 34, the end stubs of the bars23 are shown, next to them indentations 35.

As FIG. 5 reveals, the axle journal 33 to be pushed into the socket 32has at the end a snap connection 36 in the socket 32 and, what is more,a torque securement in the form of a tongue-and-groove connection, ofwhich the grooves 37 appear in the drawing.

The wheel 22 consequently has a mechanical plug connection. A plugconnection combined with the latter for the required electricalconnections is not drawn.

The wheel 22 is divided into a wheel core 38, shown in FIG. 5, and anouter part 39, shown in FIG. 6. The wheel core comprises a housing,which is rotatably mounted by bearings 40 on the axle journal 33 and inwhich there is arranged, on a stator plate 41 formed integrally with theaxle journal 33, a circular row of field poles 42 and, opposite this onthe rotatable housing, a row of magnets 43 with a back iron 44.

The outer part 39 acts with a centering fit on the wheel core 38 and hasa plurality of screw connections with the latter, in each case at aradial projection 45, said connections being evident from the relevantdrill holes 46 and being used at the same time to fasten a housing cover47 of the wheel core 38. The outer part 39 bears a flexible tire 48.

The function of the drive of the golf caddie according to FIGS. 3 to 6is the same as in the case of the golf caddie according to FIGS. 1 and2. The strain gages are merely relocated into the measuring units 25 andthe control is relocated into the case of the axle 21. A measuring unit,to be considered as similar to the measuring unit 25, can be seen inFIGS. 7 and 8.

FIG. 7 reveals a draw bar 49 and a ring-shaped handle 50, which areconnected to each other by means of bolts 51 and 52 via a molding 53 andalso by an embedding 54 of plastics compound, enclosing thisarrangement.

The molding 53 is drawn on its own in FIG. 8, on an enlarged scale.

Altogether, it comprises a flat cuboid of aluminum, in which four webs57 and four webs 58 are formed by clearances 55 and 56. Attached at thewebs 57 are four strain gages, denoted by DMS 1L to DMS 4L, attached atthe webs 58 are four strain gages denoted by DMS 1Q to DMS 3Q.

If tension occurs between the bolts 51 and 52, DMS 1L and DMS 4L arestretched and DMS 2L and DMS 3L are compressed. In the case of pressure,DMS 2L and DMS 3L are stretched and DMS 1L and DMS 4L are compressed.Transverse force of the bolt 52 with respect to the bolt 51 to the rightstretches DMS 1Q and DMS 4Q and compresses DMS 2Q and DMS 3Q. Transverseforce to the left stretches DMS 2Q and DMS 3Q and compresses DMS 1Q andDMS 4Q. The longitudinal force can be measured by a bridge circuit ofthe strain gages DMS 1L to DMS 4L, the transverse force can be measuredby a bridge circuit of the strain gages DMS 1Q to DMS 4Q. By measuringthe longitudinal force, the pulling or pushing forces acting on the drawbar 49 are determined. By measuring also the transverse force betweenthe bolts 51 and 52, i.e. between the handle 50 and the draw bar 49, thetorque transmitted from the or to the.device frame is also acquired.

The arrangement of the strain gages DMS 1L to DMS 4L and DMS 1Q to DMS4Q in the respective bridge circuit can be seen in FIG. 9. In each ofthe bridge circuits shown there, X2 and X3 denote terminals for thetapping of a measuring signal. X1 and X4 identify in both bridgecircuits a terminal connection to a voltage source (Ucc) and to ground(GND), respectively. As FIG. 9 reveals, the individual strain gages DMS1L to DMS 4L and also DMS 1Q to DMS 4Q are respectively interconnectedin such a way to form a bridge that the strain gages provided inmutually corresponding bridge branch sections are deformed in oppositedirections upon actuation of the draw bar 49. This accordingly alsoproduces an opposing changing of the resistance ratio of the straingages in the two bridge branches, which results in a considerableunbalance of the measuring bridge and consequently in a higher measuringsensitivity in comparison with a measuring bridge having a total of onlytwo strain gages, provided in one bridge branch.

Further details, concerning in particular the motor control, are nowexplained with reference to FIG. 10. In the diagram shown there, a drivemotor is denoted by the reference numeral 80, this preferably being athree-phase synchronous motor, as already mentioned in the previousdescription. The drive motor 80 is in connection with a motor operatingcircuit 81 for the direct activation of the motor 80. The motor 80 issupplied with a suitably controlled operating voltage via the operatingcircuit 81. In addition, the mode of operation of the motor, which canbe used both as a motor and as a generator, is controlled via the motoroperating circuit 81.

The motor 80 is also in connection with a rotor-position sensing device82, which constantly generates measuring signals from which therespective angular position of the rotor can be determined. Therotor-position sensing device 82 is connected to a microprocessor unit83, which receives the measuring signals generated. The microprocessorunit 83, serving as a central control device, is also connected to themotor operating circuit 81, the microprocessor unit 83 not onlysupplying signals for controlling the motor operating circuit but also,as still to be explained later, receiving signals from the motoroperating circuit. The double-headed arrow drawn in between the motoroperating circuit 81 and the microprocessor unit 83 is intended toindicate this bilateral exchange of signals.

In FIG. 10, a force measuring sensor is denoted by the reference numeral84, this preferably being one of the measuring arrangements describedabove on the basis of strain gages and, in particular, a measuringelement having at least one set of four strain gages interconnected toform a measuring bridge, according to FIGS. 8 and 9. The output signalsof the force measuring sensor 84 are fed via an amplifier circuit 85 tothe microprocessor unit 83.

A voltage supply 86, also shown in FIG. 10, includes in the embodimentdescribed here a storage battery and a switching voltage controller, fedby the storage battery, for the generation of constant supply voltages.As can be seen from FIG. 10, the supply voltage 86 supplies operatingvoltages to all the functional units 81 to 85 described, the reversesituation applying in cases in which the motor 80 operates as agenerator, with the voltage supply 86 also being fed, via the motoroperating circuit 81, a voltage, which charges the storage battery.

In the embodiment described here, the voltage supply includes asupplementary circuit, which responds to an initial generator voltage ofthe motor 80 and puts into operation, or operational readiness, theswitching voltage controller and consequently, by means of thecommencing operating voltage generation, the other functional groups 81to 85. Such an initial generator voltage is generated when a travellingdevice using the auxiliary drive described, for example a golf caddie,is set in motion. In this case, the user of the device does not need toactuate any switch to establish operational readiness. Thus, due to theautomatic switching-on, the auxiliary drive does not require any specialattention.

In travelling operation, the amplified signal of the force measuringsensor 84 is constantly available at the microprocessor 83 forprocessing and is sampled and processed according to the programming ofthe microprocessor unit. The microprocessor compares the measuringsignal of the force measuring sensor with a predetermined set value andcalculates control signals which can be used for resetting the sensorsignal to the set value. These control signals are fed to the motoroperating circuit 81 in order to control end stages of the motoroperating circuit supplying motor operating voltages, so that the motorchanges its torque according to the automatic controlling to beperformed. If the pulling or pushing force actually to be exerted formoving the travelling device lies above a predetermined pulling orpushing force to be exerted by the user, relief is provided byincreasing the torque of the drive motor and the force measuring sensorgenerates a correspondingly reduced signal. According to the automaticcontrolling, the relief continues until a match is achieved between thepredetermined set value and the force measuring sensor signal receivedby the microprocessor unit. If, on the other hand, the pulling orpushing force to be exerted does not reach the predetermined pulling orpushing force, so that it is found in the comparison in themicroprocessor unit 83 that the set value is not reached, themicroprocessor unit 83 calculates control signals for the motor 80 to beoperated as a generator, so that the motor generates a braking powersuitable for correcting the set-value deviation.

If a three-phase synchronous motor is used, the microprocessor 83calculates the control signals for controlling the phases of the motoroperating voltages in a suitable time sequence, with the inclusion ofmeasuring signals of the rotor-position sensing device, from which themicroprocessor unit calculates the angular position of the rotor. Thecalculation of the control signals fed to the motor Operating circuit 81is thus performed on the basis of the respective rotor position, therebymaking it possible at any time to set the optimum position of the rotaryfield corresponding to the rotor position and consequently to ensure amaximum applied torque on the rotor.

The rotor-position sensing device preferably comprises two analog Hallgenerators which generate two signals offset with respect to each otherby 90° with the aid of the rotor magnets or an additional magnetarrangement. On account of the orthogonality of the signals thusobtained, the magnetic rotor angle can be calculated from this in aquasi-linear form, i.e. with high resolution and an extremely shortacquisition time, with the aid of a mathematical function of the formα=arctan (a/b).

From the position signals constantly supplied in high time resolution bythe rotor-position sensing device, all further system variables, such asfor example the rotary speed, of the rotor can be determined. Fordetermining the rotary speed, the microprocessor unit 83 differentiatesthe determined positional angle of the rotor over time. In theembodiment described here, the motor control is performed exclusivelyunder program control by means of the microprocessor unit, i.e. themotor characteristic is determined by the software by which themicroprocessor unit is operated. This software solution permits a highlyefficient, quickly responding automatic control, even when there israpid changing of the pulling or pushing load. The user of a travellingdevice equipped with the auxiliary drive has the impression that thedevice always opposes a movement with the same resistance, irrespectiveof whether the movement is accelerated, retarded, uphill or downhill,and that the device can thereby be moved largely without any jerking.

In the embodiment described here, the rotor-position sensing devicecomprises Hall generators which are activated via the stator magnets oran additional magnet arrangement and from the signals of which themicroprocessor unit 83 can in each case determine the angular positionof the rotor. However, a pickup supplying counting pulses and integratedin any case in a three-phase motor could also be used for angularposition determination, it being possible for the positionaldetermination to be performed by the microprocessor unit under programcontrol by means of an upward and downward counting.

In the embodiment shown, the microprocessor unit 83 receives any errorsignals there may be from the output stages of the motor operatingcircuit 81, by means of which signals a safety shut down of theauxiliary drive can be triggered in the event of a fault.

If, as in the embodiments shown above, there are in each case two drivemotors integrated in wheels, the microprocessor calculates the controlsignals fed to the motor operating circuit 81 separately for each motor,it being possible to include in the calculation of the control signalsnot only the rotor positions but also the motor speeds, calculated fromthe rotor positions, and also signals of the force measuring sensorrepresentative of transverse forces. Consequently, different runningpaths and rotational speeds of the wheels are taken into account. In thecase of a golf caddie having two wheels, it can be additionallyachieved, in a way corresponding to the automatic control described,that turning of the caddie, and in particular turning in place, ispossible by applying a relatively small torque, to be applied by theuser, in that the turning as such is also boosted by the auxiliarydrive. When turning in place, the auxiliary drive would then drive thewheels in opposite directions of rotation.

The program control of the microprocessor unit 83 could be provided insuch a way that the set value is changed as a function of the motorspeed, and consequently as a function of the speed of the travellingdevice, in such a way that the user always has to exert the same forceirrespective of the speed with which he is moving the device. Thus, thedriving force which has to be exerted by the user at a relatively highspeed should be reduced. The microprocessor unit 83 could also beconnected to an input unit, via which the driving power to be exertedcan be set as desired.

FIGS. 11 and 12 show a wheel 59 with in addition to the motor integratedbatteries and integrated control. The motor has in principle the sameconstruction as in FIG. 5: a stator plate 61 formed integrally with anaxle journal 60 bears a row of stators 62, to which there is assigned aring of magnets 64, provided with a pole ring 63, on the rotating partof the wheel 59 designed as housing 65. The housing 65 is arranged withbearings 66 on the axle journal 60; its one wall comprises a removablehousing cover 67. A tire 68 is seated here directly on the housing 65.

An annular circuit board 70 is fastened by means of pins 69 on thestator plate 61 at some distance from it. It bears, above the dashedline in FIG. 12, the control electronics and, below the dashed line, thepower electronics, including power transistors 71 bearing against theaxle journal 60. The batteries 72 are fitted on a carrier plate 74,which is seated on the axle journal 60 and is connected by webs 73 tothe stator plate 61.

In a way similar to on the axle journal 33, provisions for a mechanicalplug connection of the wheel 59 to a device frame are conceivable on theaxle journal 60. Combined therewith is an electric plug connection 75,which provides the connection to the measuring device.

The wheel 59 is envisaged, for example, for an industrial cart.

I claim:
 1. A travelling device driven by a primary driving forceexerted by human or animal power, the travelling device comprising anelectric auxiliary drive, the auxiliary drive comprising a drive meansfor producing a driving torque for exerting a boosting effect when arequired driving force exceeds the primary driving force and forproducing a regenerative braking torque for exerting a regenerativeeffect when the required driving force is smaller than the primarydriving force, a measuring device for measuring the primary drivingforce exerted by human or animal power, and control means for adjustinga predetermined primary driving force such that, when the predeterminedprimary driving force is exceeded, the driving torque is increased orthe regenerative braking torque is decreased, and, when thepredetermined primary driving force is not reached, the driving torqueis decreased or the regenerative braking torque is increased.
 2. Thetravelling device according to claim 1, further comprising means forarbitrarily adjusting the predetermined primary driving force.
 3. Thetravelling device according to claim 1, comprising means for adjustingthe predetermined primary driving force by a control program.
 4. Thetravelling device according to claim 1, wherein the drive meanscomprises a three-phase synchronous motor.
 5. The travelling deviceaccording to claim 1, comprising a device frame and two coaxial wheelsattached to the device frame, each wheel comprising a separatelycontrolled motor, wherein proportions of the primary driving force foreach wheel are determined from a measurement of a bending moment or atransverse force occurring in the device frame.
 6. The travelling deviceaccording to claim 1, comprising an axle having a shape of an elongatedcase, gearlessly integrated motors being mounted on the axle, andwherein batteries are housed in the axle.
 7. The travelling deviceaccording to claim 1, comprising a device frame and wheels attached tothe device frame, each wheel comprising an integrated motor and anintegrated battery.
 8. The travelling device according to claim 7,wherein the motors are gearlessly integrated in the wheels.
 9. Thetravelling device according to claim 7, wherein the control means areintegrated in the wheels.
 10. The travelling device according to claim6, further comprising axle journals fastened to the axle by means ofrotationally secure plug connections, further comprising plugconnections combined with the rotationally secure plug connections forcontrol lines extending into each wheel.
 11. The travelling deviceaccording to claim 10, wherein additional supply lines extend throughthe plug connections for the control lines.
 12. The travelling deviceaccording to claim 5, wherein the device frame comprises a crosspointthrough which an entire flow of force of the primary driving forcepasses, wherein the measuring device for measuring the primary drivingforce is located in the crosspoint.
 13. The travelling device accordingto claim 12, wherein the measuring device comprises means for measuringthe bending moment and the transverse force.
 14. The travelling deviceaccording to claim 12, wherein the device frame further comprises ahandle and a draw bar extending at an angle relative to the handle, thecrosspoint being located between the handle and the draw bar.
 15. Thetravelling device according to claim 12, wherein the measuring devicecomprises a molded component, the molded component having openingsdefining webs where bending stresses are concentrated, furthercomprising strain gages attached to the webs.
 16. The travelling deviceaccording to claim 15, wherein the molded component is embedded in aplastics compound.
 17. The travelling device according to claim 12,wherein the measuring device comprises pairs of strain gages arrangednext to one another such that one strain gage is stretched when anotherof the strain gages is compressed, the strain gages being arranged in abridge circuit and a tapping point being located between the straingages.
 18. The travelling device according to claim 16, wherein theplastics compound is attached in a force-transmitting manner to thedevice frame.
 19. The travelling device according to claim 6, whereinthe travelling device is a golf cart, the device frame supporting a golfbag, the device frame further comprising two upwardly converging barsrigidly attached to the axle having the form of an elongated case, thetwo bars having outwardly bent upper ends, a draw bar being attached tothe upper ends of the bars, a handle being attached to the draw bar,further comprising a carrying rack attached at two joints to the axle soas to be swingable between a supporting position and a position in whichthe carrying rack rests against the two bars, and wherein the measuringdevice is located at a transition between the two bars and the draw bar.20. The travelling device according to claim 6, wherein the travellingdevice is a golf cart, the device frame supporting a golf bag, thedevice frame further comprising two upwardly converging bars rigidlyattached to the axle having the form of an elongated case, the two barshaving outwardly bent upper ends, a draw bar being attached to the upperends of the bars, a handle being attached to the draw bar, furthercomprising a carrying rack attached at two joints to the axle so as tobe swingable between a supporting position and a position in which thecarrying rack rests against the two bars, and wherein the measuringdevice is located at a transition between the draw bar and the handle.21. The travelling device according to claim 17, wherein the bridgecircuit comprises two pairs of strain gages, the pairs including straingages arranged diagonally relative to one another, such that one straingage of the pair is stretched when another of the pair is compressed.22. The travelling device according to claim 5, comprising a startingcircuit responding to a generator voltage of each motor for establishingan operational readiness of the auxiliary drive.
 23. The travellingdevice according to claim 5, wherein the control means comprises amicroprocessor unit for receiving a signal from the measuring device, amotor operating circuit connected to the microprocessor unit and outputstages for supplying motor operating voltages, and a device fordetermining an angular position of a rotor in each motor, themicroprocessor unit serving for calculating control signals to be fed tothe motor operating circuit including the determined angular position ofthe rotor.
 24. The travelling device according to claim 1, wherein thecontrol means comprises means for adjusting the predetermined primarydriving force such that a user of the travelling device applies aconstant driving power irrespective of the speed of the travellingdevice.